Schematics

What kind of mechanisms drove the karakuri mechanized dolls beloved by the people of Edo period Japan?We will introduce you to a breakdown of the diagram for the tea-carrying “chahakobi” doll that was restored on the basis of original schematic drawings.

The Workings of Karakuri Mechanized Dolls

1. Forward Movement - Work of the Gears

One of the doll (gears) that takes the initial force of an unwound spring has 60 teeth, and the two-wheeled sheave that receives the gear’s rotational force has 8 teeth.Accordingly, the sheave should rotate about seven times in the time it takes for the gear to make a single rotation, but it gets caught on the cam on the sixth rotation.The driving wheels that propel the doll forward has a diameter of about 10 cm, so the doll advances about 160 cm by the time the cam catches.A stopping wheel (ratchet) is attached to one wheel to prevent the spring from unwinding on its own.

2. Walking - Movement of the Legs

In the schematics, it is shown that the boards affixed to the left and right driving wheels should be affixed ahead of center on the left side and behind center on the right side.By doing so, the rotation of the driving wheels becomes a crank motion, creating a back and forth movement with the left and right working opposite each other.This section is connected to the legs of the doll and the legs step forward, giving the appearance of walking.

3. Regulators - “Koshirin” and “Tenpu”

Inside the board on the left side of the doll is a wheel called a “koshirin” (movement control wheel), which is a wheel that adopts the regulator mechanisms of clocks as is.Then, there are two claws called “tenpu” that are attached above and below the wheel that alternately catch on the teeth of the “koshirin”, producing rotations of a regular rhythm. The speed of movement of all the other doll’s mechanisms is regulated in conjunction with this movement.

The doll’s steady speed of movement hinges on the effect of this mechanism.

4. Changing Directions - Work of the Cam

A small wheel attached to the front area of the bottom board is what changes the direction the doll advances in.It performs the role of a tricycle’s front wheel, so to speak.A cam on the left side of one of the wheels (driving wheel) pushes on the left side of a handle-shaped component which determines the direction of this wheel, and as a result, the doll turns to the left.The doll continues the turning motion while the cam is working, but once the cam releases, the handle returns to its original position due to the spring effect and the doll moves forward in a straight line.

5. Switch - The Stop Mechanism

Among the movements of the tea-carrying doll, there is nothing more interesting than the mechanism that makes the doll move again once it is stopped.The secret lies in a mechanism that makes clever use of the movements of the doll’s arms.When a tea cup is placed on the tea tray, the doll’s arms lower due to the weight of the cup, turning an axle and raising a stopper.On the contrary, when the tea cup is lifted, the tips of the hands rise because of the effects of the spring, the axle turns, and the component that gets caught on the claw wheel of the “koshirin” moves down, stopping the doll’s movement.The up and down movement caused by setting down and lifting up the tea cup acts as a switch.